In some areas of technology it is necessary to guide an instrument to a target point in an object, and it is then no longer possible to observe at least the tip and part of the instrument visually once the instrument has been at least partly introduced into the object, so that some uncertainty remains as to where the instrument, in particular the tip of the instrument, is currently located within the object, and whether the current guidance direction of the instrument corresponds to the desired guidance direction of the instrument relative to the target point that the instrument was intended to reach within the object.
Such a problem area also exists in medical technology, for example in the case of punctures such as transdermal bile duct aspirations or biopsies, during which a needle is guided to a target tissue, as a rule using transillumination images, otherwise known as fluoroscopy. By using transillumination images projected from different directions, a doctor can check the position and orientation of the needle relative to the target area and guide the needle to the target area or target tissue in a patient's body. However, pinpoint guidance of the needle sometimes turns out to be challenging, since the only images that the doctor has at his disposal for checking and guiding the needle have been projected from different directions, and frequently the puncture target can be made out only indistinctly or not at all.
It has therefore been suggested that for better understanding of a patient's anatomy and the puncture target, a data set of preoperative 3D images of the puncture area should be recorded and the intraoperative transillumination images should then be registered with the 3D image data set. It then becomes possible to superimpose image data from the 3D image data set upon image data from the transillumination images, so that for example the puncture tissue or the puncture target can be displayed in the transillumination images for better control of the puncture.
Yet even when transillumination images are superimposed with image data from a preoperative 3D image, as is possible by performing a 2D-3D registration, uncertainties still remain in the course of the puncture. A transillumination image enhanced by 3D image data does in fact make the target tissue and the needle visible at the same time, but the exact position of the target tissue and the needle relative to one another is shown to only a limited extent, since as a rule the 2D transillumination image lacks not only target and separation information, but above all depth information.
Document DE 10 2005 012 985 A1 discloses a method for checking the guidance of a needle during a surgical operation on a patient; in this method a 3D image is provided showing at least the tissue area in which the operation is being carried out. A user of the system marks up the 3D image with the position of the starting point and at least the target point of the operation. A guidance path for the instrument to follow in space is automatically computed on the basis of these marks. The computed guidance path is projected and graphically displayed in transillumination tissue area images obtained intraoperatively, said guidance path taking account of the projection geometries of the transillumination images concerned. Information about how the direction of the needle needs to be corrected can also be displayed in such a transillumination image. In order to execute the method disclosed in document DE 10 2005 012 985 A1, the 3D image and the 2D transillumination images are registered with one another, as described for example in document DE 102 10 646 A1.